Year	% of revenue
1973	5.076405076405075
1974	6.66592353137889
1975	8.252988816043194
1976	10.067788099422538
1977	9.939102323133598
1978	9.804467330039648
1979	9.694108517105343
1980	11.01995041907685
1981	13.199665831244786
1982	13.524611739931613
1983	13.298851146366978
1984	14.997342610040135
1985	15.896046650443116
1986	15.44163615254086
1987	10.92842898293817
1988	9.097213192909443
1989	8.99553474660774
1990	8.976416841585381
1991	8.540097474523737
1992	8.70297384450013
1993	8.345071632253356
1994	7.890779851001348
1995	8.102342131408898
1996	8.527796088771698
1997	7.725010734069585
1998	7.275022155383088
1999	6.181445730779974
2000	6.788913369070543
2001	8.392798907786442
2002	7.272875995201221
2003	7.604752233303145
2004	8.22897384721978
2005	8.545111912575834
2006	9.229899586953426
2007	8.685040214477212
2008	10.733036274533166
2009	10.426201493989359
2010	10.193597098095214
2011	10.322210875979286
2012	10.821120337082686
2013	11.5267152023692
2014	9.264396167346552
2015	7.872575529583912
2016	6.109789320088269
2017	5.6872021631501735
2018	5.570656173645115
2019	5.012853072827893
2020	3.979181556849274
2021	4.981958233382622
2022	6.596571669499453